That sounds like an awesome tool! At some point I was back-and-forthing with my colleagues, via email, to work something out, we must’ve created a dozen gists, in the period of an hour.

I had a ten-second look at the etherpad embedding link, and it uses an iframe for it. Wouldn’t that prevent styling for the syntax highlighting? I’m not sure how that would play over iframe boundaries, since it wouldn’t be same-origin.

And to contribute: Last week I discovered that etherpad also has an export API.
If you append the pad URL with /export/txt you’ll get the raw version (also works for other formats, e.g. html, pdf, latex)

The iframe embedding may cause that kind of problem yeah. I don’t have any experience with it. Even without syntax highlighting it could still be useful, or maybe we could modify etherpad to do rust syntax highlighting and host it somewhere.

And our very own pcwalton wrote a spec for [javascript syntax highlighters to share language definition files]((https://pcwalton.blogspot.de/2010/11/syntax-highlighting-specification.html).
It seems this spec was used for Mozilla Skywriter (defunct) and the Cloud9 cloud IDE.
Cloud9 doesn’t list Rust as a supported language, but does have “see each other type” as a feature. I guess Rust support could be added?
Cloud9 seems way-overkill for a playground application though, they basically want to be your IDE, VCS and CI all in one…